audio/shortwave: re-format 18da48b5f564 patch

$ portlint -C
[...]
WARN: /usr/ports/audio/shortwave/files/patch-gstreamer-audio_src_audio__format.rs: patch was not generated using `make makepatch''. It is recommended to use `make makepatch'' when you need to [re-]generate a patch to ensure proper patch format.